This invention relates to electrolytic extraction of ionic silver from photographic, liquid fixing solutions.
The recovery of silver by electrolysis from photographic fixing solution is already well known and many systems of this type have been devised in an effort to process large quantities of liquid in a more efficient and less costly manner. However, prior systems and apparatus are characterized by various problems and disadvantages such as heavy equipment components, costly maintenance, high energy consumption and most importantly restriction of operational efficiency to a narrow range of liquid chemical properties.
The foregoing type of silver extraction apparatus usually includes a liquid tank within which an electrode assembly is suspended including at least one electrode on which the silver is electrolytically plated in response to plating current conducted through the liquid between electrodes from some source of electrical plating voltage. To enhance the electrolytic action, bladed impellers are sometimes used to agitate or augment flow of the liquid as disclosed in U.S. Pat. Nos. 4,302,318 and 4,319,971, while exhaust fans are provided for cooling purposes as disclosed in U.S. Pat. No. 4,127,465. Current control systems have been proposed to vary the plating current in order to maximize silver recovery as disclosed in U.S. Pat. Nos. 3,551,318, 3,751,355, 3,875,032, 3,925,184, 3,959,110, 4,018,658, and 4,263,108. The use of two recovery tanks through which the liquid is repetitiously processed in series, has also been proposed in U.S. Pat. Nos. 4,127,465 and 4,302,318.
It is an important object of the present invention to provide a less costly and more efficient electrolytic silver recovery apparatus which is capable of being operated with maximum efficiency for a wide variety of ionic silver containing liquids having different mineral contents, chemical composition and electrochemical properties that have heretofore affected efficient use.
An additional object of the present invention is to provide apparatus of the foregoing type which is capable of being programmed for use with optimum efficiency within threshold limits established in accordance with the particular chemistry of the liquid being processed.